The present invention relates to a fuel injection pump for an internal combustion engine, and more particularly to a fuel injection adjusting apparatus for the pump in which a hollow cylindrical fuel cut-off valve opens and closes a fuel escape port in a fuel distributing plunger which is rotationally and reciprocally driven therethrough.
U.S. Pat. No. 3,630,643 to Eheim et al discloses a fuel injection pump which includes a fuel distributing plunger which is rotationally and reciprocally driven by the rotation of a cam disc connected to a drive shaft of an internal combustion engine. When the plunger is in its rarefaction stroke, an intake groove in the plunger can communicate with a fuel inlet passage so that fuel is drawn into a working space which is compressed during the compression stroke of the plunger, so that fuel in the plunger working space is injected via an axial passage in the plunger, one of a plurality of check valves and a corresponding injector into the corresponding cylinder when the axial passage in the plunger communicates during its rotation with a corresponding fuel passage leading to the check valve.
Fuel injection by the pump terminates when fuel in the working space is vented into a chamber within the pump housing via a cut-off port provided in the plunger. The part opens and closes via axial displacement of a hollow cylindrical cut-off valve slidably fitted over the plunger.
A mechanism which controls the cut-off valve includes a pair of electromagnetic windings or solenoids wound around a C-shaped core and a magnet disposed pivotably within the magnetic field of the core. The magnet is supported by a shaft, the lower end of which carries an eccentrically mounted ball-and-socket joint in conjunction with the cut-off valve, whereby rotation of the magnet is transmitted to axially move the cut-off valve.
The electric current flowing through the pair of electromagnetic windings or solenoids and therefore the angular motion of the magnet are controlled by an amplifier in accordance with the output of a controller which receives signals indicative of operating parameters of the internal combustion engine, for example, engine speed, accelerator pedal position, air intake pressure, engine temperature, atmospheric temperature, etc.
With this conventional fuel injection pump, since the torque of the pivotting magnet is transmitted to the cut-off valve via its shaft and the eccentrically mounted ball-and-socket joint, the mechanism is considerably complicated. Also design tolerances and normal wear on the ball-and-socket joint produce errors in the displacement of the cut-off valve.
In addition, a conventional position sensor senses the position of the cut-off valve indirectly in such a manner that instead of sensing the axial displacement of the cut-off valve, the rotation of the magnet is converted into linear displacement of a ferrite core, which linear displacement is sensed by a pair of inductance coils wound around the ferrite core and energized by an oscillator. This does not result in good control accuracy.